Seasonal denitrification rates in two created riparian
marshes were investigated under pulsing and steadywater
flow conditions. Denitrification was measured using the in situ acetylene block technique. Measurements were performed in a transverse gradient with different hydrologic conditions: low marsh and open water zones
which were permanently flooded, high marsh zones which
had permanently saturated soils but standing water during pulses, and edge zones which were normally dry with standing water during flood pulses. Denitrification in all plots was significantly correlated with soil temperature and was significantly correlated with the nitrate concentration in the inflow surface water in the growing season. Late spring denitrification rates in the high marsh zone were significantly higher under flood pulsing (778 ± 92 mg N m-2 h-1) than under steady flow (328 ± 63 mg N m-2 h-1). In the low marsh and edge zones, flood pulses did not affect denitrification. N2O/N2 ratios were higher in intermittently flooded (high marsh and edge) zones than in permanently flooded (low marsh) zones and highest in the cold seasons. Highest mean denitrification rates were observed in the low marsh zone (800 ± 102 mg N m-2 h-1) and they were significantly higher (P < 0.05) than in the high marsh (458 ± 87 mg N m-2 h-1) and edge (315 ± 40 mg N m-2 h-1) zones but not significantly different from the open water zone (584
± 101 mg N m-2 h-1). Denitrification in high marsh zones was not significantly different than in the open water and edge zones. In permanently flooded areas, denitrification rates were significantly higher near the wetland inflow than near the outflow. Overall, denitrification in the experimental wetlands was 147 ± 54 kg N yr-1 during pulsing year and 112 ± 41 kg N yr-1 during steady-flow. Denitrification appeared to be nitrogen limited in low marsh, high marsh and edge
plots, but both carbon and nitrogen limited in open water.

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http://hdl.handle.net/1811/24089

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